Process for disposing solid radioactive wastes



PROCESS FOR DISROSING SOLID RADIOACTIVE WASTES I of 6 Sheet OriginalFiled Dec. 24, 1963 INVENTOR; J [/6 M o ia BY 5 /L Sky/um ATTORNEY.

ec- 19.68 SENICHI SUGIMOTO 3, ,7

' PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24.1963 Sheet 2 of 6 INVENTOR: .Sf/V/(H/ Sue/Ma 70 BY M. ATTORNEY.

D 1968 ssmcm suemcro 3,418,788

PROCESS FOR DISPQSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24.1963 Sheet ,1 of 6 INVENTOR: SIM/0W SIG/I70 7' c- 1968 szwcm SUGIMOTO3,413,788

PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES Original Filed Dec. 24.1963 Sheet 5' ore INVENTOR JA//(/// 506 /M0 in:

BY 8M S ATTORNEY.

3 1968 SENICHI SUGIMOTO 3, 18, 88

PROCESS FOR msposme soup RADIOACTIVE WASTES Original Filed Dec 24, 1963Sheet INVENTOR. f/V/CH/ JUG- lMa 70 BY 5. M gait ATTORNEY United StatesPatent 3,418,788 PROCESS FOR DISPOSING SOLID RADIOACTIVE WASTES SenichiSugimoto, Tokai-mura, Naka-gun, Ibaragi-ken, Japan, assignor to NihonGenshiryoku Kenkyujo, Tokyo, Japan, a corporation of Japan Continuationof application Ser. No. 333,063, Dec. 24, 1963. This application Sept.29, 1966, Ser. No. 583,152 Claims priority, application Japan, Dec. 28,1962, 37/59,151 3 Claims. (Cl. 558) ABSTRACT OF THE DISCLOSURE A methodfor disposing of solid radioactive wastes which comprises incinerationto effect a reduction in volume, mixing the ash with water to preventits dispersion into the atmosphere, and filtering the flue gas to removesolid particles therefrom. The filtering involves cyclone separation forthe coarser particles, electrical precipitation for finer particles,cloth filtering for the still finer particles, and high performancefiltering for the finest particles.

This application is a continuation of my earlier application, Ser. No.333,063, filed Dec. 24, 1963 and now abandoned.

This invention relates to a process for compacting solid radioactivewaste material prior to its ultimate disposal, or more particularly to aprocess for the compacting by incineration of low level radioactivewastes contained in combustible solid materials.

The radioactive solid wastes, like the radioactive liquid wastes, arewaste products inherently produced in connection with nuclear powerindustries or laboratories working with radioactive materials.

The kind, size, radioactive level or volume of radioactive wastes willvary in characteristics generally in accordance with their sources ofradioactivity. As for instance, the nuclear reactor principally produceshigh level resin or filtered material, but the laboratories handlingradio isotopes mostly discharge low level combustible or incombustiblewastes and these low level wastes form a quantitatively greaterproportion of the waste materials. Therefore, it is desirable to providean effective treatment to reduce the volume of the radioactive wasteproducts to facilitate their ultimate disposal.

There are two usual processes for the volume reduction or compactingtreatment. One is the boiling process and the other is the incinerationor burning process and the incineration method comprises the wet systemand the dry system.

Generally speaking, the boiling process has the advantages of simplicityand low cost both for installation and operation as compared with theincineration process, but it has a great disadvantage of being low inits volume reduction as compared with the dry incineration process. Thatis to say, the burning process provides a residual waste volume of /20to of the original volume, While the boiling process results in a finalresidual volume of only A1. to /6.

The present invention relates to an improved process of dry incinerationwhich has been proven to be highly efficient and economical. There isemployed an electrical precipitator in place of a venturi scrubber whichis used in a wet incinerating system. There is further applied amulti-stage cloth filter for removal of the radioactive materials in theflue gas. The precipitator is an electrostatic device in which aluminiumfoils are used as collecting 3,418,788 Patented Dec. 31, 1968 electrodesbeing rolled up, after use, into a removable roll together with thecollected dust. There is also provided a multi-stage changeable clothfilter comprising a number of stacked filtering frames and the filtercloth, such as cotton flannel is removable together with the dustcollected on the surface thereof by rolling up the cloth from one end.Each of these filters can be employed individually as a pre-filter for ahigh performance filter of the type manufactured by the Cambridge FilterCorporation, Syracuse, N.Y. When the cloth filter is connected theelectrical precipitator, the removal of dust from flue gas becomes moreeffective and sometimes will permit the Cambridge filter to be omitted.

The invention will now be more fully described with reference to theaccompanying drawings illustrating a preferred embodiment thereof.

FIG. 1 is a schematic or flow diagram of a complete incinerating systemin accordance with the invention.

FIGS. 2-4 illustrate the electrical precipitator.

FIG. 2 is a side elevational view partly shown in section along the lineIIII of FIG. 3.

FIG. 3 is a sectional view in elevation taken along the line III-III ofFIG. 2.

FIG. 4 is a perspective view of the electrode system of FIGS. 2 and 3.

FIG. 5 is a plan sectional view with the top cover portion omitted.

FIG. 6 is a sectional view in elevation taken along the lines VI-VI ofFIG. 5, looking in the direction of the arrows.

FIG. '7 is a sectional side elevational view with side wall omitted atthe inlet side.

FIG. 8 is a perspective view of the inner structure.

FIG. 9 is an enlarged cross sectional view showing four of the stackedfiltering frames.

As shown in FIG. 1, contaminated combustible wastes consisting of suchas papers, cloths, filters and miscellaneous materials are thrown intothe incinerating furnace 2 from the inlet 1 and burnt in the furnace bya gas burner 3. The gas burner 3 incinerates at a temperature of about800 C. The resulting ash is mixed with water supplied by a pipe 5 to areceiving container 22 so as to avoid its dispersion and it is collectedin an ash collecting tank 6 through an exhaust pipe 22a, while thesurplus water remaining in the ash collecting tank is delivered to thewaste water storage tank 8. The flue gas from the furnace 2 passesthrough a duct 9 to a cyclone 13. Prior to entering the cyclone 13, theflue gas is sprayed and mixed with a dilute solution of NaOH flowingthrough the pipe 12 and a nozzle 10 from the tank 11. The NaOH solutionis eflicient in neutralizing the acidity of the waste gas and it alsolowers the temperature of the waste gas by evaporation heat. The solidsin the flue gas in the form of small particles are discharged from thebottom of the cyclone 13 into the drain tank 14 through the exhaust pipe13b together with small quantities of liquid, and then transferred tothe waste liquid tank 8 through a pipe 14a. Thus the flue gas whichleaves the cyclone '13 passes into a cooler 15 through a duct 13a. Aportion of the flue gas becomes liquefied in the cooler and theliquefied material is sent to the drain tank 14, through a pipe 15b. Theremaining flue gas is delivered to a reheater 16 through a pipe 15a,where it is raised in temperature slightly and sent into the electricalprecipitator 17.

This electrical precipitator 17 is constructed as shown in FIGS. 2, 3and 4 and its operation is described in described in detail below.

The afore-mentioned flue gas enters the inlet 17a in the upper portionof the precipitator and leaves through the outlet 17b in the lowerportion. The discharge electrodes are formed by a series of verticalwires 31 which are horizontally spaced at proper intervals. The upperends of the wires 31 are suspended from a horizontal rod 34 in theprecipitator chamber, to which wires there is applied a voltage of tokv. for operation. Therefore, the support frames 34 are fixed to thecover flanges 36, 36a in the high tension chamber by insulators 35, 35awhich provide high voltage insulation. Each wire 31 of the dischargeelectrode is formed by a plurality of thin wires in order to enhancecorona discharge therefrom. The lower end of each wire 31 carries andinverted U- shaped tensioning weight 37, the legs of which straddle ahorizontal rod 38 to prevent swinging. The rod 38 is supported byinsulators 39.

In the precipitator chamber 32, there are, as shown in FIGS. 3 and 4,two horizontally spaced vertical collecting electrodes 41, 41a formed ofaluminum or other metallic foil. The collecting electrodes 41, 41a areparallel to the plane of the wires 31 and are spaced equidistantlytherefrom. The collecting electrodes 41, 41a are intially rolled up onthe rods 42, 42a located in the upper portion of the precipitator. Whenthe dust deposits sufficiently on the collecting electrodes 41, 41a,these electrodes are progressively rolled up on the rods 44, 44a locatedin the lower portion of the precipitator. The electrodes 41, 41a passover guide bars 33, 33a and are rolled up on the rods 44, 4411 with thedust collecting surface turned inward. The broken lines showntransmission chain interconnecting the guide bars 33, 33a so that theyrotate in unison. The dust in the flue gas flowing continuously intothis dust collecting chamber 32 is charged by corona discharge emittedfrom the discharge electrode wires 31 and deposits on the surface of thecollecting electrodes of metallic leaves electrostatically. Thiselectrical precipitator can separate dust having a particle size assmall as 1,, so that it is capable of removing minimal quantities ofradioactive dust. By using aluminum foil of 0.05 mm. thickness for thecollecting electrodes 41, 41a, the electrodes may readily be rolled upwithout breaking. After the dust coated aluminum foils 41, 41a have beenprogressively taken up on the bars 44 and 44a to a sufficient extent toprovide a predetermined desired minimum outside diameter for the rolledfoil, the couplings 47 are disconnected and the bars together with theirrolled foils are placed in a suitable cartridge for wastes and stored ina safe place.

The flue gas flowing out the electrical precipitator through the outlet17b is conducted to the multi-stage cloth filter 18. This filter isprovided with a plurality of inlet pipes 51, 52, 53, 54, 55, throughwhich the flue gas flows and enters stacked filter frames 60, 60a ofsquare shape. The filter frames 60, 60a are formed by rectangular pipes,as shown in FIG. 6, and, when free are supported horizontally inslightly spaced vertical relationship by strong tension springs 57, 57connected to opposite sides of each of the filter frames. Inside thefilter frames 60, 60a, there are provided a series of small holes 61arranged in horizontal rows, through which the gas enters the centralgas chamber 62 defined by the rectangular pipes forming each filterframe 60. From each chamber 62, the gas passes through a filter cloth 63closely fitted to both upper and lower faces of the filter frame 60 andenters the outlet chambers 64 defined by the frames 60a each disposedabove one of the filtering frames 60. The inlet gas chambers 62 and theoutlet gas chambers 64 are of the same size and construction. Each ofthe inlet pipes 51 to 55 communicates with one of the gas chambers 62and each of the outlet pipes 71 to 75 communicates with an outletchamber 64. Therefore, the gas delivered from the electricalprecipitator 17 flows from the inlet chambers 62 to the outlet chambers64 passing through the filter cloth 63. The stacked filtering frames 60,60a are pressed downwardly against a bottom supporting plate 59 by alever 65 controlled by a hand wheel 66 by a top pressure plate 58. Thispressure assures gastightness for the inlet and Outlet chambers.

In order to change the filter cloth, the hand wheel 66 is turnedreversely, so that the top pressure plate 58 is released and thefiltering frames 60, 60a become supported by suspension springs 57 andthe contact between the filter cloth 63 and filtering frames 60, 60a isbroken. This permits the filter cloth to pass freely between the frames60, 60a so that the used cloth may be rolled up. In this case anymaterial may be chosen for the filter cloth, but preferably it isdesirable to use rolls of flannel cloth of standard size usually sold onthe market (0.68 m. x 45 m.). This is mounted on the supply roll shaft76 and passes upwardly in a serpentine configuration around verticallyspaced guide rods 77, 78 provided at the right and left sides,respectively, of the stacked frames as shown in FIG. 7. It is led frombeneath the pressure plate 58 to receiving shaft 79 turned by a handwheel 80. The used filter cloth 63 is rolled up and, together with itsrod 79 stored for ultimate disposal.

The gas, after passing through the multi-stage filter 18 is discharge bya blower 20 into the exhaust air pipe 21, as shown in FIG. 1, afterpassing through a further filter 19 which is a conventional CambridgeFilter.

During this process, the electrical precipitator 17 and the cloth filter18 work as prefilters for the Cambridge filter 19. By this prefiltering,the useful life of the Cambridge filter 19 becomes longer and itsoperation is more economical than if the wet system is used.

According to the past operation, it is known that the dust content ofthe filter 19 is decreased to a greater extent when the cloth filter 18is connected in series behind the electrical precipitator 17 than whenthe cloth filter 18 is used separately without the precipitator 17.

It seems to be that the small dust particles in the flue gas becomeaggregated by the corona discharge, forming larger composite particleswhich are readily filtered by By the afore-mentioned device, theradioactive waste dust is effectively completely removed from theincinerator flue gas containing radioactive materials. The final dustremoval operation using the high performance filter 20 is effective tobring the total removal to 99.9%.

While I have shown and described what I believe to be the bestembodiment of my invention, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

What is claimed is:

1. The method for concentrating and accumulating solid radioactive wastematerial for ultimate disposal which comprises the steps of:

(l) incinerating combustible waste material containing said radioactivewaste material in a furnace to produce a coarse ash which falls to thebottom of said furnace and a flue gas containing fly ash;

(2) adding water to said coarse ash;

(3) passing said gas from said furnace to the inlet of a cycloneseparator while spraying a dilute solution of sodium hydroxide into saidcyclone inlet;

(4) passing said gas through said cyclone;

(5) separating water and fly ash from the gas as its passes through thecyclone;

(6) collecting the separated water and fly ash;

(7) passing the gas from the cyclone to a cooler;

(8) cooling the gas in the cooler to condense at least some of thecondensible components of the gas;

(9) collecting the condensed components;

(10) passing the gas from the outlet of the cooler to the inlet of anelectrostatic precipitator;

(ll) reheating the gas during the course of its passage from the coolerto the precipitator;

(l2) collecting particles of fly ash on metallic foils within theprecipitator;

(13) progressively rolling up the metal foils during the course of saidparticle collection;

(14) removing the rolled foils for ultimate disposal;

(15) collecting other fly ash particles from the bottom of saidprecipitator;

(16) passing gas from said precipitator to filter means including aporous filter cloth;

(17) accumulating fly ash particles on said cloth;

(18) progressively winding up said cloth during said accumulating step;

(19) removing the wound up cloth for ultimate disposal;

(20) passing said gas after passage through said cloth from said filtermeans to high performance filter means; and

(21) discharging said gas after passage through said high performancefilter means into the atmosphere.

2. The method according to claim 1, comprising the further step of:

(22) passing the watered coarse ash from the furnace, the water and flyash from the cyclone, the condensed components from the cooler and thefly ash particles from the precipitator to common storage means.

3. The method according to claim 2, comprising the further steps of:

(23) providing means for selectively by-passing the gas around theprecipitator;

(24) providing means for selectively by-passing the gas around thefilter means having a filter cloth; and

(25) providing means for selectively by-passing the gas around the highperformance filter means.

References Cited UNITED STATES PATENTS 643,022 2/ 1900 Wilson 210-255964,725 7/ 1910 Whiting 210-227 2,186,501 1/1940 Seligman et al. 210-230X 2,303,262 11/ 1942 Dumire 2103 87 X 2,522,568 9/1950 Dahlman 2103 87 X2,535,697 12/1950 Roos 149 X 2,714,849 8/ 1955 Carver 210231 X 2,752,0036/ 1956 Hersey et al. 55354 X 2,840,454 6/ 1958 Tomlinson, et. al.2,851,124 9/1958 Howell 557 2,932,399 4/ 1960 Emele 210225 2,958,392 11/1960 Dietrich 55-126 2,983,234 5/1961 Reilly -165 3,028,714 4/1962 Mayer55--116 X 3,261,149 7/1966 Althuser 55354 FOREIGN PATENTS 534,950 3/1941 Great Britain.

551,815 3/ 1943 Great Britain.

692,565 6/ 1953 Great Britain.

842,669 7/1960 Great Britain.

63,554 6/ 1941 Norway.

HARRY B. THORNTON, Primary Examiner.

D. TALBERT, Assistant Examiner.

U. S. Cl. X.R.

